I believe why the Bronco is so stable on ice in a straight line is, the 
front turns at a slightly greater speed than the rear axles. The front 
an rear differentials are the same ratios, the transfer case has a 
timing chain that has slightly different number of teeth on the main 
drive, and the front drive. This is good gear and chain design practice 
so the chain "hunts", doesn't always mesh the same teeth, but every 
revolution is over a tooth or 2. Yea, the terms part-time and full-time 
four wheel drive are really misnomers. The Bronco is considered 
part-time, the transfer case full disconnects the front driveshaft from 
the tranny, and hard connects when in engaged, no fluid, slip clutches 
or differentials. The better gas mileage results when both the transfer 
case and front hubs are disengaged and the front differential gears are 
not turning. I'm amazed at the number of Dodge pickups I follow, and am 
able to see the front U-joints turning, even on bright sunny days, a 
vehicle that looks like it never will get near the mud. :)

Eoin Ross wrote:
> My old Discovery has a "centre diff lock" that locks up the transfer case diff - otherwise its permanent 4WD, it only binds up like yours when that is locked. Same issues in a Suzuki Samurai, Subaru Leone/DL, Suzuki XL7 - anything that locks front/rear drive together.
>
> It's due to the front and rear driveshafts turning at the same speed, even though the front needs to go faster. The hops come from the driveline forces building up and overcoming the tyre/ground forces, relieving the pressure in a "hop", then building up again. Much like earthquakes from a faultline.
>
>   
>>>> cdenk@alltel.net 26 Jan 08 12:30:41 >>>
>>>>         
> The 1996 Bronco with manual hubs and transfer case (part time), 
> <snip>
> On tight corners on dry, locked up, slow speed, sometimes can feel tires slipping, kind of like a 
> hop, probably part due to the non-constant velocity cross/yoke U-joints. 
> <snip>
>
>
>   
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